1. Field of the Invention
The present invention relates to a technique for controlling the operation of a pump; and more particularly, the present invention relates to a method and apparatus for controlling a pump, e.g., for domestic and commercial heating or cooling water systems.
2. Brief Description of Related Art
By way of example, FIG. 1(a) shows a secondary variable speed pump control hydronic heating and cooling system that is known in the art, and FIG. 1(b) shows a water booster pumping system that is also known in the art. Recently, issues regarding energy saving and environmental protection in such pumping systems have been addressed dramatically. Increasing more attention is being paid to hydronic pump control applications, including pump controls for domestic and commercial heating and cooling water pumping or circulating systems, water booster pumping systems, and so forth, like those shown in FIGS. 1(a) and (b) with their characteristics that may be dynamic and unknown in nature. To reduce energy consumption and operation costs, some known adaptive control approaches have been proposed.
Furthermore, the aforementioned U.S. patent application Ser. No. 12/982,286, filed 30 Dec. 2010 discloses an adaptive control scheme for hydronic heating and cooling pumping systems as well as for water booster pumping systems, consistent with that shown in FIGS. 1(a) and (b) schematically. In FIG. 1(b), the hydronic pumping system includes a controller and a pump arranged in relation to a process pipe having check valves configured therein. In operation, the pump responds to control signaling from the controller, and pumps the a flow through the process pipe. FIG. 1(c) shows a graph having various functions plotted using known system curve equations, e.g., including a pump curve, an instant system curve, a constant control curve, an equivalent system curve (as designed), an adaptive control curve and a distribution loss curve. A pressure set point, P*, with respect to a flow rate requested, Q*, can be calculated and/or determined from the equation of P*(t)=(Q*(t)/Cva(t))2+b, where the adaptive control curve, Cva(t), may be obtained from the flow equation together with a moving average filter. With this adaptive approach, the adaptive control curve to obtain the pressure set point is much closer to the equivalent system curve which represents the minimum pressure needed to maintain the flow rate requested, consistent with that shown in FIG. 1(c). Because of this, pumping system operation energy may be saved using this adaptive approach.
Moreover, techniques are known in the art for using sensorless pump conversion to obtain system pressure and flow based upon motor readouts signals. However, known sensorless models presented so far are formulated in either a 1D space or a 2D discrete space, which makes it a difficult to obtain the system pressure and flow rate from motor speed and power in terms of algorithms development and signals conversion accuracy.
Several know approaches may be used for the sensorless conversion, including discrete models calibrated with pump and system hydronic data together with numerical solutions. Such discrete sensorless modeling approaches are simple and straightforward. The conversion accuracy may be preserved well within a less than 5-10% margin of error. On the other hand, there are some theoretical approaches as well based upon pump and system characteristics equations for some simple and easy pump control applications where there is no accurate flow and pressure for pump control requested and there is no calibration sensors provided. As a tradeoff, the flow and pressure conversion accuracy may have as low as a greater than 10-15% margin of error. However, the conversion accuracy may be deteriorated very rapidly at low speeds.